Infrared Thermography for Simultaneous Detection of Limb Pathology and Subclinical Mastitis in Dairy Cows

This study evaluated infrared thermography (IRT) as a dual-purpose, non-invasive tool for detecting limb pathology and subclinical mastitis in dairy cows. Surface temperatures were measured at the coffin, pastern, and fetlock regions of all limbs and at the teat surface of all udder quarters. Limb health status was determined by orthopedic clinical examination, and mastitis status was assessed using the California Mastitis Test (CMT). Hindlimbs were significantly warmer than forelimbs in healthy cows (p < 0.001), with confirmed bilateral symmetry (r = 0.524-0.569). Limbs with pathology showed significantly higher temperatures at all anatomical sites, with particularly large effect sizes in the hindlimbs (r around 0.80). Additional lesion-specific analyses demonstrated that both infectious and claw horn lesions exhibited significantly higher temperatures than healthy limbs. In the hindlimbs, infectious lesions showed higher thermographic values than claw horn lesions. CMT-positive quarters showed teat temperatures of 30.0-30.2 °C compared with 25.2-25.8 °C in CMT-negative quarters (p < 0.001). Receiver operating characteristic (ROC) analysis demonstrated excellent diagnostic performance for teat surface temperature in identifying CMT-positive quarters, with an area under the ROC curve (AUC) of 0.956. The optimal threshold was 29.5 °C, corresponding to a sensitivity of 0.992 and a specificity of 0.838. Each 1 °C increase in teat temperature increased the odds of CMT positivity by 5.3-fold (p < 0.001). A practical three-zone thermographic framework was established: <27 °C (healthy), 27-29.5 °C (monitoring recommended), and ≥29.5 °C (mastitis likely). Teat temperature was not associated with composite milk somatic cell count, but hindlimb pathology was independently associated with elevated teat temperatures (partial r = 0.23-0.26, p ≤ 0.001). These findings demonstrate that IRT has strong potential as an integrated screening tool for dairy cow limb health and udder health monitoring.